He doesn't get the purpose of marriage , why not?

Julio and I have been dating for about fourteen months, I'm 21 and he is 28. We dated pretty seriously but made it known he did not want to get married or have anymore children. I stayed even though I knew I wanted this, dealt with his racist mother and crazy family in hopes he would eventually change his mind. I gave this man my virginity my heart pretty much everything. My mom hated him and caused me to be kicked out of her house. I got my own place and lived on my own.
Well Julio and I broke up for two months and recently got back in contact. He admitted he bought me a Tiffany's ring and threw it out once I had said I couldn't be with him. He said he was miserable without me and wanted to give me whatever my heart desires kids and marriage. He owned up to all his faults and has really implemented a change in himself but he did admit he didn't understand the idea of marriage but would do it if it meant having me in his life.

Why would someone get married if they don't believe in the idea?